Infimum and supremum of empty set

AI Thread Summary
The infimum of the empty set is defined as infinity (inf∅ = ∞) to ensure consistency in calculations involving subsets. If inf∅ were assigned a finite value, it would create contradictions with the infimum of sets containing elements. Similarly, the supremum of the empty set is defined as negative infinity (sup∅ = -∞) to maintain coherence in mathematical operations. This approach effectively removes the empty set from influencing the calculations of infimum and supremum. The definitions serve to streamline mathematical reasoning involving these concepts.
strobeda
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Hello,

I can't wrap my mind around this:

inf∅= ∞
sup∅= - ∞

Thank you in advance.
 
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inf∅ is artificially defined to be ∞ so that inf will work well. Suppose we had defined inf∅ = 998 and we had a set with one element, 999. Then we want inf({999}) = 999. But since ∅ is also a subset of {999}, we would have inf({999}) = inf∅ = 998. The only way to avoid this problem is to make inf∅ greater than any possible number. So inf∅ = ∞. Similarly we have to define sup∅ smaller than any possible number. So sup∅ = -∞.

In a sense, this is just getting ∅ out of the way of the calculation of inf and sup.
 
Indeed, it gets ∅ out of the way!

Thank you very much, FactChecker!
 
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